This is Matrise’s glossary, which provide definitions for commonly used terms, technical concepts and abbreviations within the topic of Virtual Reality.

Presence, within Virtual Reality (VR), usually refers to the psychological sense of feeling present (“feeling there”) in the virtual environment. It is convenient to separate between ‘presence’, and ‘immersion’, which often are used interchangeably.

Immersion, sometimes defined as ‘technological’ immersion, is an objective measure of sensory fidelity afforded by the virtual reality application. Slater and Wilbur (1997) defines immersion in terms of four qualities the system can afford: inclusiveness; extensiveness; the degree of surrounding or encapsulation; and vividness. They write: “Inclusive (I) indicates the extent to which physical reality is shut out. Extensive (E) indicates the range of sensory modalities accommodated. Surrounding (S) indicates the extent to which this virtual reality is panoramic rather than limited to a narrow field. Vivid (V) indicates the resolution, fidelity, and variety of energy simulated within a particular modality (for example, the visual and color resolution)“

Degrees of Freedom (DOF) refers to the number of positional or rotational parameters that the user can alter by input to the system. For instance, with 3DOF, the degrees a user can manipulate can be summarized as rotation in 360 degrees, without any positional manipulation (by physical movement). The three degrees refer to roll, pitch and yaw. 6DOF on the other hand, include add the 3D positional attributes of forward/back, left/right, and up/down.

High refresh rates are a requirement to reduce motion sickness in VR, and today HMDs usually have close to 100Hz of refresh rate. However — refresh rates alone are not enough to reduce the motion blur which end up causing motion sickness. Most popular VR HMDs also use other solutions in combination, that enables low pixel persistence by means of software, and not simply by increasing refresh rates. We often call these «Low Pixel Persistence Modes».Rejhon (2013) explains that 1 ms of pixel persistence equals 1 pixel of motion blur during 1000 pixels/second. In theory this means that to achieve a low pixel persistence of 1ms, one would need a 1000 Hz screen to manage it. By the same math, a 60Hz LCD screen by nature offers 16 ms motion blur (16 * 60). According to Abrash (2014), 3ms motion blur should be maximum to ensure a subjective feeling of presence, and this would require several hundred frames per second, which is why pixel persistence can not be fixed through refresh rates alone.

Pixel persistence can be defined as how long a pixel persists on displaying the same image. This is obviously very closely related to refresh rates, as the higher refresh rate you have, the less time each pixel will persist in displaying itself. Yet, pixel persistence differ from refresh rate in that it is not how often the pixel changes, but for how long it is displayed. Pixel persistence may then vary between systems of equal refresh rate. When utilizing pixel persistence modes, the light of the screen is turned off between each pixel change, so that each pixel is visible for a shorter period of time, reducing the pixel persistence and thus reducing the amount of time each pixel is not corresponding to the physical movements of the user. This is the key to how a lower pixel persistence will aid in the quest to eliminate cybersickness. At BlurBusters.com, you can see examples of how these low pixel persistence modes effectively reduce motion blur. They explain the problem with the normal modes as their tendency to sample-and-hold.

Eye Tracking in VR has other benefits than only research-analytical purposes. Through a technique called “foveated rendering”, the data from the eye tracking is used to decide which areas of the screen that is most important to render at high quality. What is in the periphery of our vision, may not require the same supersampling as what is in the centre of our vision. This may be a technique of increasing importance in the future, as VR is very demanding in terms of graphical power. As of 2018, the use of this is not very widespread yet. There are several startups who the latest years have claimed to be close to a release of eyetrackers to about $200, and time will tell how this will work out in the future.

The uncanney valley effect is a hypothesised interrelation between the degree to which a humanoid object resembles an actual human being, and the emotional response that this generates in real human beings. Put shortly, people report feelings of horror and uncanniness when perceiving a humanoid object that very closely resembles human beings — but yet not perfectly. This feeling may be exaggerated in VR, as one may feel more close to the humanoid object which triggers this emotional response, or feel “trapped in the Uncanney Valley”. Would you like to experience it yourself? Here are 10 examples of the Uncanney Valley.

The screen door effect is an unwanted effect that occurs when a user sees the space in between the pixels in the Head-Mounted Display. This may decrease feeling of presence and realism, as it becomes apparent that one is staring at a screen. Generally, one may say that the lower the resolution of the display, the more likely it is that the user is able to see the gap between the pixels of the display. For instance, the Vive has far worse screen door effect than the Vive Pro. Yet, this is not the only indicator, and there are “Anti-SDE” technologies such as in the Playstation VR and Odyssey+ that can help to reduce the effect. Although the Vive has a higher resolution than the Playstation VR, the screen door effect is lower in the Playstation VR, and the visuals (may) therefore be more enjoyable.

Not yet added to the glossary:

Augmented Reality (AR) refers to the concept of augmenting the physical world with virtual phenomena. We separate between mobile AR, which uses smartphones, tablets and their cameras to combine the physical and virtual — and see-through Head-Mounted Displays such as the Microsoft Hololens, which project virtual images on a see-through holographic display.